Re: PR 90409 Deque fiil/copy/move/copy_backward/move_backward/equal overloads

["Daniel Krügler" <daniel.kruegler@gmail.com>]

Am Do., 1. Aug. 2019 um 13:01 Uhr schrieb Jonathan Wakely <jwakely@redhat.com>:
>
> On 01/08/19 12:36 +0200, Daniel Krügler wrote:
> >Am Do., 1. Aug. 2019 um 11:57 Uhr schrieb Jonathan Wakely <jwakely@redhat.com>:
> >>
> >> More comments inline below ...
> >[..]
> >>
> >> >François
> >> >
> >> >On 6/19/19 7:32 PM, François Dumont wrote:
> >> >>I wanted to implement Debug overloads for those already existing
> >> >>overloads but then realized that those algos could be generalized.
> >> >>This way we will benefit from the memmove replacement when operating
> >> >>with C array or std::array or std::vector iterators.
> >> >>
> >> >>I might do the same for lexicographical_compare one day.
> >> >>
> >> >>The ChangeLog below is quite huge so I attached it. I wonder if I
> >> >>could use deque::iterator and deque::const_iterator in place of the
> >> >>_Deque_iterator<> to reduce it ?
> >> >>
> >> >>Tested under Linux x86_64 normal and debug modes, ok to commit ?
> >> >>
> >> >>François
> >> >>
> >> >
> >>
> >> >diff --git a/libstdc++-v3/include/bits/deque.tcc b/libstdc++-v3/include/bits/deque.tcc
> >> >index 3f77b4f079c..9db869fb666 100644
> >> >--- a/libstdc++-v3/include/bits/deque.tcc
> >> >+++ b/libstdc++-v3/include/bits/deque.tcc
> >> >@@ -967,155 +967,507 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> >> >       this->_M_impl._M_finish._M_set_node(__new_nstart + __old_num_nodes - 1);
> >> >     }
> >> >
> >[..]
> >>
> >> And anyway, isn't _Deque_iterator<T, T&, T*>::_Self just the same type as
> >> _Deque_iterator<T, T&, T*> ? It should be something like:
> >>
> >>       typedef typename _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*> _Iter;
> >>
> >> >+  template<typename _II, typename _Tp>
> >> >+    typename enable_if<
> >> >+      is_same<typename std::iterator_traits<_II>::iterator_category,
> >> >+            std::random_access_iterator_tag>::value,
> >>
> >> Use is_base_of<random_access_iterator_tag, ...::iterator_category> so
> >> it works for types derived from random_access_iterator_tag too.
> >
> >Interesting. Traditional type tag dispatching approaches (as function
> >parameters) do have more in a manner that would be equivalent to an
> >implicit conversion (Being used as "by-value-parameters"), so I'm
> >wondering whether this should not instead refer to is_convertible? I
> >also found examples where this trait is currently used in <stl_algo.h>
> >such as
> >
> >      static_assert(
> >      __or_<is_convertible<__pop_cat, forward_iterator_tag>,
> >        is_convertible<__samp_cat, random_access_iterator_tag>>::value,
> >      "output range must use a RandomAccessIterator when input range"
> >      " does not meet the ForwardIterator requirements");
> >
> >Should possibly this trait be preferred?
>
> Hmm, I don't know why I did it that way in sample.
>
> The standard requires derivation in a couple of places today, see
> [reverse.iterator] bullet 2.1 and [move.iterator] bullet 1.1 which use
> DerivedFrom<random_access_iterator_tag> to check whether the base
> iterator is random access or not.

If you want to mimic DerivedFrom you also need to include
is_convertible in some way, because is_base_of does not care about
access. Maybe introduce __is_derived_from?

- Daniel